Three-position (catalectic) verses in fornyrðislag are fully integrated with their regular, four-position counterparts, and accordingly composed in strict conformity to the four-position principle through alignment of the verse-final drop with null linguistic material. However, they are produced only exceptionally in violation of the same principle in Beowulf and Genesis A. With maximal fidelity to the principle, Beowulf almost categorically disallows such short verses, whereas Genesis A, constrained by the principle to a lesser extent, is more liberal in accepting them, as with other metrical operations controlled by the canon, such as anacrusis. Far from random accidents, however, these anomalous verses are most likely to arise under a cluster of syntagmatic conditions: i) The missing element constitutes a verse-final drop; ii) it is preceded by two consecutive lifts. Given the two forces working in optimal combination, the configuration PPx occurs with the highest incidence among the variants of three-position verses in these two Old English poems.